Engineering task and calculation objective
The FRIG module provides thermophysical properties of refrigerants for the thermal design of evaporators, condensers and refrigeration plants. If you need to calculate refrigerant properties — such as density, specific heat capacity, thermal conductivity, viscosity, surface tension or enthalpy of vaporization — you obtain them here as functions of temperature and pressure for liquid and vapor, optionally directly at saturation on the boiling line.
Both the classic and the currently common working fluids are available: the HFCs R 23, R 32, R 134a, R 152a and R 142b, the HCFC R 22 (for existing plants), the natural hydrocarbons R 290 (propane), R 600 (n-butane), R 600a (isobutane) and i-pentane, as well as the blends R 404A, R 410A and R 507. The calculation methods are based on the standard reference Reid/Prausnitz/Poling, "The Properties of Gases and Liquids" (McGraw-Hill, 4th and 5th editions).
In addition to the transport and caloric properties, the module delivers derived quantities such as Prandtl number, thermal diffusivity, isentropic exponent and compressibility factor, as well as the critical data and the molar mass — the input quantities for heat transfer correlations in boiling and condensation and for cycle calculations.
Standard and calculation basis: Reid R. C., Prausnitz J. M., Poling B. E. "The Properties of Gases & Liquids", McGraw Hill, 4. Auflage 1987 Poling Bruce E., Prausnitz John M., O'Connell John P. "The Properties of Gases & Liquids", McGraw Hill, 5. Auflage 2001
Calculation workflow
- Select the refrigerant: The refrigerant is chosen from the built-in property database by substance name, e.g. R 134a, R 290 or the blend R 410A. This fixes the molar mass, the specific gas constant and the critical data (critical temperature, critical pressure, critical density).
- Specify the state: The user enters temperature and pressure for the liquid and/or the vapor phase. Alternatively, the saturation state is selected via the option "calculate saturation state?": then only one of the two quantities is needed, and the corresponding saturation value is determined from the vapor pressure curve.
- Calculate thermal and caloric properties: The module calculates density, specific heat capacity (cp and cv), specific enthalpy, isentropic coefficient cp/cv, compressibility factor and coefficient of thermal expansion for both phases using the correlations from Reid/Prausnitz/Poling.
- Determine transport properties and dimensionless numbers: Thermal conductivity, dynamic and kinematic viscosity, and surface tension are determined; from these, the Prandtl number and thermal diffusivity follow as dimensionless and derived quantities for heat transfer calculations.
- Use the results in follow-up calculations: The property values serve as input for the design of evaporators and condensers (e.g. nucleate boiling and condensation correlations), for pressure drop calculations in refrigerant lines, and for the energy assessment of the refrigeration cycle.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Name of substance | Stoffname | - |
| Temperature | ϑ1 ϑ2 | °C |
| Temperature | ϑ1 ϑ2 | °C |
| Pressure | p1 p2 | Pa |
| Pressure | p1 p2 | Pa |
| Density | ρ1 ρ2 | kg/m³ |
| Density | ρ1 ρ2 | kg/m³ |
| Density | ρ1 ρ2 | kg/m³ |
| Density | ρ1 ρ2 | kg/m³ |
| Specific heat capacity | cp1 cp2 | J/(kg·K) |
| Specific heat capacity | cp1 cp2 | J/(kg·K) |
| Specific heat capacity | cp1 cp2 | J/(kg·K) |
| Specific heat capacity | cp1 cp2 | J/(kg·K) |
| Dynamic viscosity | η1 η2 | mPa·s |
| Dynamic viscosity | η1 η2 | mPa·s |
| Dynamic viscosity | η1 η2 | mPa·s |
| Dynamic viscosity | η1 η2 | mPa·s |
| Kinematic viscosity | ν1 ν2 | m²/s |
| Kinematic viscosity | ν1 ν2 | m²/s |
| Kinematic viscosity | ν1 ν2 | m²/s |
| Kinematic viscosity | ν1 ν2 | m²/s |
| Thermal conductivity | λ1 λ2 | W/(m·K) |
| Thermal conductivity | λ1 λ2 | W/(m·K) |
| Thermal conductivity | λ1 λ2 | W/(m·K) |
Calculation options
Calculate boiling state?
No · Yes
Calculate boiling state?
No · Yes
Frequently asked questions
What does "near-azeotropic blend" mean for R 404A and R 410A?
Blended refrigerants generally do not evaporate and condense at constant temperature, but over a temperature glide between the bubble and dew lines. For near-azeotropic blends such as R 410A, this glide is very small (below approx. 0.2 K), for R 404A somewhat larger; the azeotropic R 507 behaves practically like a pure substance. For equipment design this means: for blends with a noticeable glide, the saturation temperatures for dew point and bubble point must be distinguished, otherwise the temperature approaches of heat exchangers are evaluated incorrectly.
Why are saturation-state properties so important for evaporator design?
Heat transfer correlations for nucleate boiling and flow boiling require the properties of the boiling liquid and the saturated vapor at saturation pressure: the densities of both phases, enthalpy of vaporization, surface tension, viscosity and thermal conductivity. If values at a different temperature or in a subcooled state are used instead, the calculated heat transfer coefficients can deviate substantially from reality. The option "calculate saturation state" provides exactly these consistent saturation values.
May R 22 still be used for new designs?
No. R 22 is a partially halogenated chlorofluorocarbon (HCFC) and has been banned in the EU since 2015 even as recycled material for service purposes; new plants using it are not permitted. However, its property data remain relevant for the rating and retrofit of existing plants, for instance when checking how a replacement refrigerant affects the capacity and pressure drop of an existing evaporator. The high-GWP HFCs (e.g. R 404A) are also subject to the F-gas phase-down and are increasingly being replaced by low-GWP alternatives.
What must be considered for the hydrocarbons R 290, R 600 and R 600a?
Propane, n-butane and isobutane are excellent refrigerants with very low global warming potential, but they are flammable (safety group A3). Their use requires charge limitation, explosion protection assessments and compliance with the relevant safety standards (e.g. EN 378). Thermodynamically they offer high enthalpies of vaporization and favorable transport properties, which often allows smaller charges and good heat transfer.